the desire to abolish freedom of religion
Part of Stalin's form of communism was to encourage loyalty to the leader and the country not to a god.
The Great Purge focused on changing the old traditions of Russia in particular those coming from monarchy. Farms were taken into control by the government and redistributed. The industrial systems went under government control and were regulated by government agents. In addition Stalin wanted to change cultural parts of the USSR to reflect the mission of the Soviet government. Requiring members of the country to be fully loyal to the country meant giving up religion and an institution which would give a higher direction or rule than the government.
